Method and apparatus for supporting amd re-segmentation

ABSTRACT

A method and apparatus for acknowledge mode data (AMD) re-segmentation are disclosed. An AMD protocol data unit (PDU) is generated from at least one RLC SDU. The AMD PDU size is within a flexible maximum AMD PDU size. The original AMD PDU is stored in a retransmission buffer, and transmitted. If transmission of the original AMD PDU fails and the original AMD PDU size is larger than an updated maximum AMD PDU size, the original AMD PDU is segmented to segmented AMD PDUs. If transmission of one of the segmented AMD PDUs fails, the original AMD PDU may be re-segmented to smaller size AMD PDUs.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/023,547, filed on Jan. 31, 2008, which claims the benefit of U.S.provisional application No. 60/887,667 filed Feb. 1, 2007, which isincorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to wireless communications.

BACKGROUND

Some of the goals of high speed packet access (HSPA) evolution includehigher data rates, higher system capacity and coverage, enhanced supportfor packet services, reduced latency, reduced operator costs andbackward compatibility. Meeting these goals requires evolutions to theradio interface protocol and network architecture. More specifically,meeting these goals has required a set of enhancements and architecturechanges to layer 2 radio link control (RLC) and medium access control(MAC) functionalities.

In universal terrestrial radio access (UTRA) Release 6, an acknowledgedmode (AM) RLC entity performs segmentation and concatenation of RLCservice data units (SDUs) into fixed-size RLC packet data units (PDUs).The RLC PDU size is semi-static and can only be changed via higher layersignaling. The AM RLC entity is always re-established if the AM PDU sizeis changed by the higher layer. However, in the evolved HSPAarchitecture, in order to support high data rates, it has been proposedto have a flexible RLC PDU size that varies to reflect channelconditions. A flexible RLC PDU size increases RLC transmission andretransmission efficiency.

Flexible RLC PDU size will allow the radio network controller (RNC) tocreate RLC PDUs that closely reflect the channel conditions. Aone-to-one mapping between an RLC PDU and a MAC PDU achieves the highesttransmission efficiency. A bigger RLC PDU size may have a detrimentaleffect on the RLC transmission efficiency in bad channel conditions.Having a flexible PDU size would eliminate this problem since for thefirst RLC PDU transmission the size will reflect the current specifiedchannel conditions, (i.e., max RLC PDU size).

However, when the RLC PDU size of the retransmission is larger than thecurrent specified maximum RLC PDU size, a problem may occur forretransmission of the RLC PDU. If the channels conditions changedramatically the large RLC PDU may never be successfully transmitted. Inaddition, when a handover from Release 7 to Release 6 occurs, RLC PDUscreated in Release 7 RLC might be larger than the new fixed RLC PDUsize.

SUMMARY

A method and apparatus for acknowledge mode data (AMD) re-segmentationare disclosed. An AMD protocol data unit (PDU) is generated from atleast one RLC SDU. The AMD PDU size is within a flexible maximum AMD PDUsize. The original AMD PDU is stored in a retransmission buffer, andtransmitted. If transmission of the original AMD PDU fails and theoriginal AMD PDU size is larger than an updated maximum AMD PDU size,the original AMD PDU is segmented to segmented AMD PDUs. If transmissionof one of the segmented AMD PDUs fails, the original AMD PDU may bere-segmented to smaller size AMD PDUs.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings wherein:

FIG. 1 is an example acknowledged mode (AM) RLC entity supporting RLCre-segmentation; and

FIG. 2 is an example AM RLC entity supporting RLC re-segmentation inaccordance with the second embodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

The following terminology will be used in this disclosure. An originalRLC PDU means the first transmitted RLC PDU. A segmented RLC PDU means afirst segmented RLC PDU of the original RLC PDU. A re-segmented RLC PDUmeans a second or later segmented RLC PDU of the original RLC PDU.Sub-segments mean segments of the segmented RLC PDU or re-segmented RLCPDU. The embodiments disclosed herein are applicable to both uplink (UL)and downlink (DL).

FIG. 1 is an example AM RLC entity 100 supporting RLC re-segmentation.The AM RLC entity 100 may be included in a WTRU or a network node,(e.g., a radio network controller (RNC) or Node-B, or any other networknode). The AM RLC entity is configured for flexible RLC PDU sizeoperation, where the AMD PDU size is variable between a minimum andmaximum RLC PDU size. The maximum RLC PDU size used throughout thisinvention can be a semi-static parameter configured by a radio resourcecontrol (RRC) or a variable sized determined by the transmitter andadapted to radio conditions.

The AM RLC entity 100 includes a transmitting side 100 a and a receivingside 100 b. A peer AM RLC entity also includes a transmitting side and areceiving side. In the transmitting side 100 a, the AM RLC entity 100receives RLC SDUs from upper layers through an AM-service access point(SAP). The RLC SDUs may be stored in a transmission buffer 102 prior tosegmentation and/or concatenation. The RLC SDUs are delivered to asegmentation/concatenation entity 106 via a multiplexer 104.

The RLC SDUs are segmented and/or concatenated by thesegmentation/concatenation entity 106 into AMD PDUs of a flexible lengthas specified by an RRC entity or a Node-B. The segmentation and/orconcatenation of RLC SDUs is performed as in conventional art. Aftersegmentation and/or concatenation, an RLC PDU header is added by an RLCheader insertion entity 108.

The RLC PDU is then sent to a transmission buffer 116 via a multiplexer114. The RLC PDU is also stored in a retransmission buffer 110 forretransmission. The multiplexer 114 multiplexes RLC PDUs from theretransmission buffer 110 that need to be retransmitted and the newlygenerated RLC PDUs delivered from the segmentation/concatenation entity106.

A retransmission control entity either 112 deletes or retransmits theRLC PDUs buffered in the retransmission buffer 110 based on the statusreport sent by a peer AM RLC entity. The status report may contain apositive acknowledgement (ACK) or a negative acknowledgement (NACK) ofindividual RLC PDUs received by the peer AM RLC entity. If a NACK isreceived for a particular RLC PDU, the retransmission control entity 112may either retransmit the RLC PDU directly via the multiplexer 114, ormay send the RLC PDU to the segmentation/concatenation entity 106 viathe multiplexer 104 for re-segmentation of the RLC PDU. When the RLC PDUin the retransmission buffer 110 needs to be retransmitted, (i.e., aNACK is received), the retransmission control entity 112 determineswhether the RLC PDU size is greater than the current (updated) maximumRLC PDU size at the time retransmission is necessary. The RLC PDU sizemay be simply compared to the maximum RLC PDU size. Alternatively, theretransmission control entity 112 may determine whether a difference ofthe RLC PDU size and the maximum RLC PDU size exceeds a threshold value,(i.e., (the RLC PDU size−the maximum RLC PDU size)>a threshold value).The retransmission control entity 112 may also determine whether thenumber of re-segmentation of the RLC PDU has exceeded a maximum allowednumber.

If the RLC PDU size is not greater than the current maximum RLC PDUsize, or the number of re-segmentation has exceeded the maximum allowednumber, the RLC PDU stored in the retransmission buffer 110 is forwardeddirectly to the transmission buffer 116 for retransmission. If the RLCPDU size is greater than the current maximum RLC PDU size and the numberof re-segmentation has not exceeded the maximum allowed number, the RLCPDU or the RLC SDU corresponding to the RLC PDU may re-segmented, whichwill be explained in detail below.

A header setting entity 118 completes the AMD PDU header of the RLC PDUstored in the transmission buffer 116. The AMD PDU header is completedbased on the input from the RLC control unit 134 that indicates thevalues to set in various fields, (e.g., polling bit). The header settingentity 118 also multiplexes, if required, control PDUs received from theRLC control unit 134, (e.g., RESET and RESET ACK PDUs), and from areception buffer 128, (e.g., piggybacked STATUS or STATUS PDUs), withRLC PDUs. The RLC PDU may be ciphered by a ciphering entity 120. Thetransmitting side 100 a of the AM RLC entity 100 submits AMD PDUs to alower layer through a logical channel, (e.g., dedicated control channel(DCCH) and dedicated traffic channel (DTCH)).

In the receiving side 100 b, the AM RLC entity 100 receives the AMD PDUsthrough the configured logical channels from the lower layer. A receivedACK is delivered to the retransmission control entity 112, and the AMDPDUs are routed to the deciphering entity 124 or to the RLC control unit134 via the demultiplexer 122. The RLC PDUs are deciphered by thedeciphering entity 124 (if ciphering is configured), and then deliveredto the reception buffer 128.

The AMD PDUs are placed in the reception buffer 128 until a complete RLCSDU has been received. The retransmission control entity 126 in thereceiving side 100 b of the RLC entity 100 acknowledges successfulreception of an AMD PDU, or requests retransmission of a missing AMD PDUby sending a STATUS PDU to the transmitting side. An RLC header isremoved by an RLC header removal entity 130. If a piggybacked STATUS PDUis found in the received AMD PDU, it is delivered to the retransmissioncontrol entity 112 of the transmitting side 100 a of the AM RLC entity100 to purge the retransmission buffer 110 of positively acknowledgedAMD PDUs, and to indicate which AMD PDUs need to be retransmitted. Oncea complete RLC SDU has been received, the associated AMD PDUs arereassembled by the reassembly entity 132 and delivered to upper layersthrough the AM-SAP.

The receiving side 100 b of the RLC entity 100 may reassemble segmentedRLC SDUs or (re)segmented RLC PDUs, and report status of the segmentedRLC SDUs or (re)segmented RLC PDUs to the peer RLC entity.

Re-segmentation of RLC PDU or RLC SDU and header formats are explainedhereinafter.

In accordance with a first embodiment, the RLC PDU stored in theretransmission buffer 110 is re-segmented to fit into the new maximumRLC PDU size. An original RLC PDU is stored in the retransmission buffer110 at the time of initial transmission. If the original RLC PDU is notsuccessfully transmitted, the original RLC PDU is retransmitted. If, dueto the change of the maximum RLC PDU size, the original RLC PDU size isgreater than the current maximum RLC PDU size (and optionally the numberof re-segmentation has not exceeded the maximum allowed number), theoriginal RLC PDU is delivered to the segmentation/concatenation entity106 and segmented into smaller size segmented RLC PDUs. The segmentedRLC PDUs are stored in the retransmission buffer 110.

To support segmentation of the original RLC PDU, additional headerinformation may be included in the segmented RLC PDU. The sequencenumber (SN) of the original RLC PDU is reused for all segmented RLCPDUs. The header information of the original RLC PDU has to be includedat least in one of the segmented RLC PDUs. A segmentation fieldindicating the segmented RLC PDUs may be included, (e.g., two or threebits to indicate up to 4 or 8 segments). A field indicating the lastsegment of the original RLC PDU may be included. Alternatively, a fieldindicating the number of segments of the RLC PDU may be included.

In addition, an indication that the current packet is a segmented RLCPDU may be included. Several options are possible for this indication. Acurrently reserved bit sequence of the header extension (HE) field inthe conventional RLC header may be used. For instance, the sequence “11”is currently reserved. The sequence “110” may be used to indicate thatthe PDU is a segmented RLC PDU, while the sequence “111” is reserved forfuture use. Alternatively, a special bit sequence may be used for thelength indicator, followed by the flag for the last segment.Alternatively, a 1 bit field (segmentation flag) may be added to the RLCheader for the new version of the RLC protocol for this purpose (thisfield may be present in every RLC PDU).

The first embodiment may be applied to re-segmentation of the originalRLC PDU and sub-segmentation of the segmented RLC PDU. When thesegmented RLC PDU needs to be retransmitted and the segmented RLC PDUsize is greater than the current maximum RLC PDU size, the segmented RLCPDU may be further re-segmented, (i.e., sub-segmentation). Allsub-segments are stored in the retransmission buffer and are discardedwhen an ACK for each sub-segment is received from the peer RLC entity.

To support re-segmentation of the segmented RLC PDUs, the followinginformation may be added to the header of the sub-segments.

-   -   Sub-segment information. Sub-segment information describes the        segment such that the receiving entity can reconstruct to the        segment or original PDU. This information may include any of the        following: total number of segments (or sub-segments), segment        number (or sub-segment number), segment size (or sub-segment        size), segment (or sub-segment) start byte (indicating the        position of the first byte of the segment of the segmented        packet or original PDU), segment (or sub-segment) last byte        (indicating the position of the last byte of the segment of the        segmented packet or original PDU), etc. A limit to the amount of        times re-segmentation is performed may be configured;    -   An indication that the packet is a sub-segment, (e.g., a bit        appended to the RLC PDU segment indication); and    -   A field indicating the number of sub-segments.

If the segmented RLC PDU size exceeds the current maximum RLC PDU size,the original RLC PDU may be segmented once again in a different RLC PDUsize, (i.e., re-segmentation), instead of sub-segmenting the segmentedRLC PDU. The re-segmented RLC PDUs are stored in the retransmissionbuffer 110 for retransmission. The segmented RLC PDU or segments of thefirst or previous segmentation are discarded from the retransmissionbuffer 110. For re-segmentation purpose, the original RLC PDU may bemaintained in the retransmission buffer. To support this scheme, aversion indicator is added to the header information of the re-segmentedRLC PDU to indicate the segmentation version of the RLC PDU, (i.e., thenumber that the RLC PDU has been segmented). Every time the original RLCPDU is segmented or re-segmented, the version indicator is incrementedby one. A limit to the number of segmentation may be configured(depending on the number of bits allocated for the version indicator, 1or 2 bits may be used).

FIG. 2 is an example AM RLC entity 200 supporting RLC re-segmentation inaccordance with the second embodiment. In accordance with a secondembodiment, a negatively acknowledged RLC PDU at the time the maximumRLC PDU size is reduced in the retransmission buffer 210 is moved to thesegmentation/concatenation entity 206 and processed as a new RLC SDU.The negatively acknowledged RLC PDU is processed in the same way asnormal RLC SDUs, (i.e., segmented and/or concatenated), except for anindication in the header. The encapsulated PDUs resulting from thisscheme are assigned normal sequence numbers, (i.e., following the samesequence as other RLC PDUs). Preferably, only negatively acknowledgedPDUs whose length is higher than the current maximum RLC PDU size areencapsulated.

The AM RLC entity 200 is substantially the same as the AM RLC entity100, except an encapsulated PDU reassembly entity 240. The receivingside 200 b of the AM RLC entity 200 places the received encapsulatedPDUs in a separate reassembly buffer (not shown) instead of placing themin the normal reception buffer 228. The encapsulated PDU reassemblyentity 240 reassembles the encapsulated PDUs. When reassembly of theencapsulated PDUs are complete, the underlying PDU, (i.e., thenegatively acknowledged RLC PDU), is moved into the reception buffer 228and successful reassembly is indicated to the transmitting side 200 a ofthe AM RLC entity 200 for acknowledgement of the underlying RLC PDUsequence number.

In order to unambiguously indicate the first and last PDUs encapsulatingthe negatively acknowledged RLC PDU, the transmitting side 200 a of theAM RLC entity 200 may be constrained to use consecutive sequence numbersfor the encapsulating PDUs, and indicate the last encapsulating PDU witha flag, (e.g., one bit), to allow the receiving side of the peer AM RLCentity to determine at which point reassembly can be completed.

The header information for the encapsulating RLC PDU is same to theconventional RLC header except that an indication is added to indicatewhether the incoming PDU is a normal RLC PDU or an encapsulating RLCPDU. Several options are possible for this indication. A currentlyreserved bit sequence for the HE field in the RLC header may be used.For instance, the sequence “11” is currently reserved. The sequence“110” may be used to indicate that the PDU encapsulates a segment of apreviously negatively acknowledged RLC PDU, while the sequence “111” isreserved for future use. An additional bit after the sequence mayindicate whether the PDU contains the last segment of the encapsulatedPDU. A special bit sequence may be used for the length indicator,followed by the flag for the last segment. A 1 bit field (encapsulationflag) may be added in the header for the new version of the RLC protocolfor this purpose, (this field may be present in every RLC PDU), followedby a flag for the last segment for these PDUs which have theencapsulation flag set.

In accordance with a third embodiment, if the RLC PDU size is greaterthan the maximum RLC PDU size when an RLC PDU needs to be retransmitted,the AM RLC entity 100 may re-segment the RLC SDU corresponding to thatRLC PDU. One extra field is added to the RLC header to indicate versionof RLC SDU segmentation. The new RLC PDUs are stored in theretransmission buffer 110. RLC PDUs corresponding to older versions ofthe RLC SDU are discarded.

In addition, if the original RLC PDU contains several RLC SDUs and/orsegments of RLC SDUs, and the original RLC PDU is larger than themaximum RLC PDU, the RLC PDU may be assembled differently. The SDUscontained in the original RLC PDU may be combined and/or segmenteddifferently to fit into the new maximum RLC PDU size. This scheme maynot support RLC PDU SN reuse. Therefore, new SDU sequence numbers orpacket data convergence protocol (PDCP) SN re-use may be applied.

The receiving side 100 b of the RLC entity 100 is responsible forreporting status information of AMD PDUs. The status reports may varydepending on which segmentation scheme is used. The status report may betriggered as in the prior art. The number of retransmission and discardtimers may be directly related to the original RLC PDU, or may beindependent for each segment, or a combination of the two. Optionally, amaximum RLC PDU size change may trigger the RLC receiver to send astatus report to the RLC transmitter.

A status report may be sent on a segmented RLC PDU basis, (i.e., segmentlevel based status), if the original RLC PDU has been segmented. Thestatus report may include an SN, a segment information, (i.e., number),and/or a sub-segment information, (i.e., number). If all segments aresuccessfully received, the status report may include only the SN, andthe peer RLC entity may deduce that all segments corresponding to thatSN are successfully received and discard all segments corresponding tothe SN in the retransmission buffer.

Alternatively, a status report may be sent once all segments of theoriginal RLC PDU have been received successfully. The status report issent on an RLC PDU basis, (i.e., no segment information), asconventionally done, (i.e., sequence number is indicated in the statusreport). If the RLC receiver detects that a segmented RLC PDU has beenreceived with an updated version indicator, the RLC receiver may discardall successful RLC PDUs which contain an older version indicator.

In status reporting of re-segmented RLC SDUs, the status report may beRLC SDU-based or RLC PDU-based. If the RLC receiver detects that adifferent version of the RLC PDU has been received with an updatedversion indicator, the RLC receiver may discard all successful RLC PDUswhich contain an older version indicator.

Although the features and elements are described in embodiments inparticular combinations, each feature or element can be used alonewithout the other features and elements of the embodiments or in variouscombinations with or without other features and elements. The methods orflow charts provided may be implemented in a computer program, software,or firmware tangibly embodied in a computer-readable storage medium forexecution by a general purpose computer or a processor. Examples ofcomputer-readable storage mediums include a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

1-12. (canceled)
 13. A method for acknowledgement mode (AM) radio linkcontrol (RLC) segmentation, comprising: generating, using a RLC entity,a RLC protocol data unit (PDU) from at least one RLC service data unit(SDU); segmenting the RLC PDU to generate a RLC PDU segment of a firstsize, wherein the first size is within a maximum size associated with afirst transmission opportunity; including header information in the RLCPDU segment, wherein the header information comprises a sequence number(SN) of the RLC PDU; transmitting the RLC PDU segment; receiving astatus report to indicate a transmission status of the RLC PDU segment;re-segmenting the RLC PDU segment to generate a re-segmented RLC PDU ofa second size, wherein the second size is within a maximum sizeassociated with a second transmission opportunity; and transmitting,using a transmitter, the re-segmented RLC PDU.
 14. The method of claim13, wherein header information of the RLC PDU is included in the RLC PDUsegment.
 15. The method of claim 14, wherein the sequence number (SN) ofthe RLC PDU is included in an RLC header of the re-segmented RLC PDU.16. The method of claim 13, wherein the first size of the re-segmentedRLC PDU is determined by the transmitter.
 17. The method of claim 13,further comprising storing the RLC PDU segment in a retransmissionbuffer.
 18. The method of claim 17, wherein the status report comprisesa negative acknowledgement (NACK) from a peer RLC entity.
 19. The methodof claim 18, wherein the status report further comprises the SN of theRLC PDU.
 20. The method of claim 13, further comprising receiving astatus report for the re-segmented RLC PDU comprising the SN of the RLCPDU and sub-segment information of the re-segmented RLC PDU.
 21. Themethod of claim 13, further comprising receiving a positiveacknowledgement from a peer RLC entity for the re-segmented RLC PDU. 22.A user equipment (UE) having computer circuitry to: generate a radiolink control (RLC) protocol data unit (PDU) from a RLC service data unit(SDU); segment the RLC PDU to generate a RLC PDU segment of a firstsize, wherein the first size is determined by a transmitter operablycoupled to the computer circuitry; include header information in the RLCPDU segment, wherein the header information comprises a sequence number(SN) of the RLC PDU; transmit the RLC PDU segment to a receiver; receivea status report comprising a negative acknowledgement (NACK) for the RLCPDU segment; re-segment the RLC PDU segment to generate a re-segmentedRLC PDU of a second size, wherein the second size is within a maximumsize associated with a second transmission opportunity; includesub-segment information in each re-segmented RLC PDU, the sub-segmentinformation comprising a segmentation field, a segment start field, anda segment last field to indicate a position of the re-segmented RLC PDUin the RLC PDU; and transmit the re-segmented RLC PDU to the receiver.23. The UE of claim 22, further comprising a display, a memory, aspeaker, and a microphone.
 24. The UE of claim 23, further comprising aBlue-tooth module and a wireless local area network (WLAN) module. 25.The UE of claim 24, wherein the receiver is a base station.
 26. One ormore non-transitory computer readable media with executable instructionsstored thereon that, when executed, cause a user equipment (UE) to:generate a radio link control (RLC) protocol data unit (PDU) from an RLCservice data unit (SDU), the RLC PDU being within a first maximum RLCPDU size for a first transmission opportunity; store the RLC PDU in abuffer; send the RLC PDU to a segmentation entity to generate segmentedRLC PDUs if a status report comprising a negative acknowledgement (NACK)is received for the RLC PDU and a size of the RLC PDU is greater than asecond RLC PDU size for a second transmission opportunity; store thesegmented RLC PDUs in the buffer; and transmit the segmented RLC PDUs.27. The media of claim 26, wherein header information of the RLC PDU isincluded in each RLC PDU segment.
 28. The media of claim 27, wherein thesequence number (SN) of the RLC PDU is included in an RLC header of eachsegmented RLC PDU.
 29. The media of claim 26, wherein the size of theRLC PDU is determined by a transmitter.
 30. The media of claim 26,further comprising receiving a positive acknowledgement for eachsegmented RLC PDU.
 31. The media of claim 26, further comprisingtransmitting the RLC PDU.
 32. The media of claim 26, wherein the statusreport further comprises the SN of the RLC PDU.